The present invention relates generally to a clockspring connector, and, more specifically to a clockspring connector that is capable of conducting high current and high numbers of circuits while keeping operational noise low. A clockspring connector is a device that allows for an electrical connection between two members that are rotatable relative to each other. One common use for the clockspring connector has been in the steering units of automobiles.
Two common clockspring designs are the cassette type clocksprings and loop back (or fold back) clocksprings. Both designs use flat flexible cables (xe2x80x9cflex cablesxe2x80x9d) to pass current between two connector portions that are rotatable relative to one another. In both designs, the flex cables have one end connected to a first portion of the connector, e.g., the inner housing or hub, and the other end of the flex cable is connected to the other housing portion, e.g., the outer housing or shell.
In the cassette type design, the flex cable is wound in a continuous circular path within an accommodating space that is defined between the first and second housing portions. As the housing portions rotate relative to each other in one direction, e.g. clockwise, the flex cable winds or accumulates around the inner housing. When the connector portions are rotated in the opposite direction, the flex cable unwinds to permit rotation of the housing portions relative to each other.
By contrast, in a loop back design, each cable has a first portion wound around the outer annular wall of the accommodating space in a first direction. The cable then loops back and extends into a second portion that is wound around the inner annular wall of the accommodating space in a second direction opposite the first direction. Loop back designs are advantageous over cassette type designs because they significantly reduce the length of cable that is required versus a cassette design. In a typical application, a loop back design uses approximately one third as much cable as a cassette type design. Since the flex cable is a relatively expensive component, loop back designs may provide a significant cost savings in comparison to cassette type designs.
Clockspring connectors are commonly used to pass current to devices, such as horn switches and cruise control switches and radio controllers, carried by the steering wheel on an automobile. As automobiles are designed with a growing number of features, it becomes necessary to increase the number of current paths (circuits) that can be carried by a clockspring connector. In order to accommodate more circuits, multiple flex cables have been used in clockspring connectors. Each cable carries one or more current paths. In many applications, it is not possible to use multiple flex cables in a cassette type clockspring connector because of size limitations on the overall envelope of the connector""s housing. Hence, where multiple cables are required, a loop back clockspring connector is typically employed.
Many loop back clockspring connectors use a cable guiding mechanism (sometimes referred to as a carrier assembly) having upstanding rollers rotatably mounted on the base. Examples of this type of design are shown in U.S. Pat. Nos. 5,637,005 and 5,865,634. In such a design, the flex cables loop around individual rollers on the guiding mechanism.
In automobile applications, a clockspring connector is typically required to turn a total of 5 turns of rotation between its travel limits, namely, two-and-a-half turns both clockwise and counterclockwise from the neutral or zero position when the steering wheel of a vehicle is turned. When a loop back clockspring connector is turned, the cable is either winds around the inner or outer wall of the accommodating space, depending on the relative position of the connector portions and their direction of rotation. For example, as the cable winds around the inner wall of the accommodating space, the layers of cable accumulate (get thicker) in the inner space defined between the guiding mechanism and the inner wall. At the same time, the cables unwind from the outer wall of the accommodating space and empty from the outer space defined between the guiding mechanism and the outer wall of the accommodating space. As this occurs, the layers of cable will have tendency to move radially inward or outward, depending of the position and direction of rotation, to balance the inner and outer spaces of the accommodating space. Known clockspring connectors have a one-piece guiding mechanism, which cannot move radially inwardly or outwardly. As a result, when the cables move radially inwardly or outwardly, they impinge upon the carrier causing the cables to buckle and prevent normal operation of the clockspring connector.
It is also known to provide a loop back design that does not employ a guiding mechanism. Examples of such a design are shown in U.S. Pat. Nos. 4,978,191; 5,409,389; 5,310,356 and 5,888,084. In these patents, the clockspring uses four cables that balance one another during operation of the connector. However, in applications where only a single cable is required to satisfy the circuit requirements, these connectors still require three flex cablesxe2x80x94one active cable and three xe2x80x9cdummyxe2x80x9d cables. Another problem with this design is that the cables can go out of balance, e.g., collapse, during operation, thereby rendering the connector inoperable. These designs may also require the use of a sticky grease to cause the flex cables to adhere to one another. Using such a grease is messy and undesirable, both during assembly and operation of the connector.
Automobiles also have an increasing number of applications where it is necessary to carry a relatively high current across a clockspring connector. One example of an increasingly common feature that requires the use of high current is that of the heated steering wheel. Conventional clockspring connectors are not well-suited for high current applications because the high current can overheat the flex cables, causing them to delaminate. As a result, slip rings have typically been used in high current applications. However, slip rings have a tendency to produce noise and to wear down over time. Operation noise is undesirable in automobile application, particularly in luxury brands where purchasers place a premium on quiet passenger cabins.
Therefore, it is desirable to provide a clockspring connector addresses the above and other problems with known clockspring connectors. In particular, it is desirable to provide a clockspring connector that is capable of conducting high current and high numbers of circuits without generating high temperatures. It is also desirable to provide a clockspring connector that reduces operational noise.
A clockspring connector according to certain aspects of an embodiment of the present invention comprises a housing, at least two guiding mechanisms, and at least two flexible cables. The housing includes at least two sections that define an annular accommodating space and that are rotatable with respect to one another. In one embodiment, a first housing section may comprise a base and a cover, while a second housing section comprises a hub rotatably mounted between the base and the cover. The guiding mechanisms are disposed in the accommodating space and can move radially inwardly and outwardly within the accommodating space. Each guiding mechanism includes a base and at least one roller rotatably connected to the base. The guiding mechanism may also include flexible members that engage the housing, so as to restrict vertical movement of the carrier in the accommodating space, thereby reducing noise during operation of the clockspring. The guiding mechanisms divide the accommodating space into inner and outer portions, the sizes of which depend upon the radial position of the guiding mechanisms within the accommodating space. Each cable has one end fixed relative to the first housing section and the other fixed relative to the second housing section. The cables extend within the outer space in a first direction. Each cable then passes between two of the adjacent guiding mechanisms and loops back around one of the rollers and extends in the inner accommodating space in a second direction opposite the first direction. Using multiple guiding mechanisms that can move radially inwardly and outwardly prevents the problems associated with prior loop back clockspring connectors that employ a single guiding mechanism. The clockspring connector also includes features that divide high current into multiple reduced current paths within the connector, which reduces temperatures within the connector.